CHICAGO (AP) — President Barack Obama's campaign is launching a new offensive Monday against Republican Mitt Romney, blasting the GOP nominee for criticizing Americans who don't pay income taxes without having "come clean" about his own.

The campaign started the new push with a television advertisement, its first spot using Romney's comments that 47 percent of voters pay no income tax, and believe they are victims and entitled to government assistance. The ad was to begin airing in Ohio — a crucial swing state where Romney was campaigning this week — but was also expected to be part of the campaign's final push elsewhere between now and Election Day.

"Maybe instead of attacking others on taxes, he should come clean on his," the ad's narrator says of Romney.

The 30-second spot signaled that Obama would keep making Romney's taxes a campaign issue. The Republican hopeful has released only two years of tax information about his personal fortune and finances.

Six weeks out from the election, Obama holds a slim lead over Romney in most battleground states. The Republican is seeking to right his campaign following a rough stretch that included the release of his secretly recorded remarks about the 47 percent and criticism that he's not campaigning hard enough for the White House.

Romney acknowledged Sunday that he was trailing the president in several key states. But he promised to spend less time courting donors and more time with voters.

"I know that in the coming six weeks they're very unlikely to stay where they are today," Romney said of the polls.

The Republican was scheduled to campaign Monday in Colorado, where aides added a rally in an attempt to deflect the criticism from within his own party. Romney was also to join running mate Paul Ryan in Ohio on Tuesday for a bus tour.

Romney senior adviser Ed Gillespie said the GOP ticket would give voters more specific details on their economic plans in the campaign's closing weeks.

"Voters will get to know more not only about the specifics of the Romney plan, but how it will benefit them," he said. "A real recovery will improve the quality of life for working Americans, and lift millions out of poverty by making jobs available again."

Obama will spend Monday and Tuesday tending to official duties at the United Nations. But his condensed schedule at the annual gathering of world leaders underscored that his focus is largely on the campaign.

Voters in more than two dozen states are already casting ballots in early voting for the presidential election, meaning everything the candidates do now could influence votes already being cast.

Obama's campaign sees Romney's remarks about 47 percent of Americans as an opportunity to solidify its lead, building on the campaign's efforts over the summer to paint the Republican as a multi-millionaire elitist who is out of touch with middle class Americans. The campaign's new 30-second ad opens with a video of Romney telling donors at a private fundraiser about the 47 percent of Americans he believes will vote for Obama no matter what.

"My job is not to worry about those people," Romney says in the video, which was taped without his knowledge.

A narrator in the Obama ad responds: "Isn't it the president's job to worry about everyone?"

Romney said he was talking to donors about campaign strategy and making the point that about 47 percent of voters won't cast their ballots for him. He has insisted following the video's release that as president, he would work for all Americans.

The Obama ad also references details about Romney's personal tax returns, including his disclosure that he and wife Ann Romney paid an effective tax rate in 2011 of 14.1 percent. That rate is lower than millions of middle-income Americans, but actually more than Romney had to pay.

The tax documents released Friday show Romney, one of the wealthiest candidates ever to seek the presidency, paid nearly $2 million in federal taxes on $13.7 million in income. Romney's income was from investment returns, which are taxed at a lower rate than income that comes mostly from wages.

Republicans argued that it was time for Democrats to stop focusing on Romney's taxes now that he has released his 2011 returns.

Romney released his 2010 returns in January, but he continues to decline to disclose returns from previous years — including those while he worked at Bain Capital, the private equity firm he co-founded. The Obama campaign and other Democrats note that Romney's father, George Romney, released a dozen years of returns when he ran for president.

The Republican nominee has made clear that he's looking to next month's three presidential debates to help him get on track. The first debate is on Oct. 3.

Romney told reporters Sunday that Obama has been "trying to fool people into thinking that I think things I don't. And that ends I think during the debates."

And he blamed his recent struggles, in part, on what he described as a series of factually inaccurate attacks from Obama.

"He keeps on running these things even though he knows they are wrong," Romney said. "Whether it's on the auto industry, whether it's on taxes, whether it's on social issues, what he's saying about my positions is simply not true."